Green Machine: Solar skylight takes the heat off

Even in an air-conditioned office, sitting near a window with direct sunlight can get pretty toasty. Now a skylight that captures the boiling rays to make electricity could keep the heat out.

Developed by Enfocus Engineering, based in Hayward, California, the device is made of an array of glass lenses that concentrate direct sunlight onto narrow, opaque strips of photovoltaic cells made of gallium-arsenide and germanium.

Light streams through traditional skylights in strong beams that heat
indoor air and change intensity as the sun moves throughout the day. Enfocus's lenses, by contrast, allow some light to pass through each lens, providing even illumination for a room without increasing the heat load in a building. And each lens can pivot independently to track the sun across the sky.

The lenses also work on cloudy days, company founder Jason Lu says. While they don't generate much electricity, the lenses still allow diffuse light to stream into the room below. "The light level does not change substantially when a cloud comes in," he says.

The units aren't in production yet, but the company plans to sell them to retrofit skylights in large commercial buildings, he says, adding that the cells could provide more electricity
than regular solar cells. Glass-walled buildings like airport terminals would benefit from them as well, where the arrays could cut electricity costs, provide natural light, and curb excess heating.